1. Field of the Invention
The present invention relates to a face opposing type motor used in a device rotated at a high speed. More particularly, the present invention relates to a face opposing type motor in which an accuracy in rotation of the motor and reliability of the motor are improved and manufacturing cost of the motor is reduced.
2. Description of the Related Art
A face opposing type motor is generally used in many cases to make various kinds of products compact and especially thin.
In such a general face opposing type motor, an aluminum alloy is used for a flange to reduce inertial force of rotation. Accordingly, a coefficient of thermal expansion of the flange is large and a coefficient of thermal expansion of a rotor magnet is greater than that of the above aluminum alloy. Therefore, when a polygon scanner using this motor is continuously operated, the rotor magnet is expanded in a diametrical direction thereof by an increase in temperature of the rotor magnet and centrifugal force of the rotor magnet so that the rotation of a rotating body is gradually unbalanced and an accuracy in rotation of the rotating body is reduced.
Further, a center of gravity of the rotating body is located in a position from an approximately central position of a dynamic pressure air radial bearing to a free end of a fixed shaft. Therefore, the rotation of the rotating body tends to be influenced by vibration of the fixed shaft so that the rotation of the rotating body is vibrated by the vibration of the fixed shaft, thereby reducing an accuracy in rotation of the rotating body.
The fixed shaft is fixed by shrinkage fit to a housing to which a casing is fitted. Namely, a dimensional tolerance for an inclination of the fixed shaft is strict with respect to an attaching reference face of the casing and a window for deflection. However, the attaching reference face and the window for deflection are fixed to the fixed shaft through the housing. Therefore, it is difficult to precisely distribute the dimensional tolerance to the reference face and the window so that an accuracy in processing of each of parts is strict and cost of the motor is increased.